The adhesion to the vessel wall and extravasation of circulating tumor cells (CTC) is a complex interplay between hydrodynamic shear forces and chemical receptor-ligand binding kinetics, and is critical to the hematologic spread of many metastatic cancers including those originating from prostate, breast, colon, and skin. Consistent with the overarching organizational framework of this proposed Center, Project 3 will deconvolve the complexity of metastatic cell adhesion in the bloodstream by utilizing experimental and theoretical approaches derived from the physical sciences. A major question that we will address is: Can CTC adhesion to the vessel wall and extravasation be understood as a multistep cascade, similar to leukocyte recruitment in inflammation? The proposed research is organized around three specific aims. Aim 1: Application of a multiscale model to predict rolling and firm adhesion of circulating tumor cells. The multiparticle adhesive dynamics simulation with stochastic selectin:carbohydrate and MUC1:ICAM-1 binding will be used with input parameters obtained from primary tumor cells isolated from the blood of metastatic cancer patients. Aim 2: Characterization of the adhesion of CTCs to defined molecular surfaces and endothelial cell monolayers under physiological shear stress. Cancer cells spiked into whole blood will be perfused through microfluidic flow chambers to test adhesion predictions of Aim 1 and identify differences between microvascular endothelial cells from different tissues. Aim 3: Study of CTC adhesion, mechanical plugging and extravasation in a live animal model. Fluorescently labeled cancer cells will be observed in the microvessels of mouse brain and skull using multiphoton intravital microscopy, to determine the relative importance of adhesion receptors and mechanical plugging in tumor cell recruitment from the bloodstream. Taken together, the proposed research will lead to new pathways to intervene in the development of cancer, such as the quantitative evaluation of biomolecular targets for. disrupting metastatic cell adhesion.